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    <h1 id="main-heading" class="ank-student jpk-modal">Learn Web Development at Udacity</h1>
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    // 将类的列表存储在一个变量中
    const listOfClasses = mainHeading.className;

    // 打印出字符串 "ank-student jpk-modal"
    console.log(listOfClasses);
    const arrayOfClasses = listOfClasses.split(' ');
    console.log(arrayOfClasses);
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